Selective hydrocracking process for converting heavy oils to middle distillates



3,513,085 HEAVY N. L. KAY

May 19, 1970 SELECTIVE HYDROCRACKING PROCESS FOR CONVERTING OILS T0 MIDDLE DISTILLATES Filed NOV. l, 1967 O O O- 2;\D\\ A /500 0.5/6

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505a oowaaa #@3522 xwwm INVENTOR. /V/C/y/OLS L, /647 United States Patent O U.S. Cl. 208-112 10 Claims ABSTRACT OF THE DISCLOSURE Heavy mineral oils boiling in the 700-1000 F. range are selectively converted to middle distillates boiling in the 3D0-700 F. range with a minimum production of lighter hydrocarbons, by contacting the feed under hydrocracking conditions with a relatively non-acidic, hydrofning type catalyst comprising nickel plus molybdenum and/ or tungsten supported on an essentially alumina carrier. In a preferred aspect high quality diesel fuel is produced as the major product, product quality being maintained essentially constant over a long run length with progressively increasing temperatures by operating at pressures above about 2000 p.s.i.g. Hydrogen consumption is minimized by employing a nitrogen-contaminated feedstock and adjusting hydrocracking conditions so that denitrogenation of the feedstock is incomplete.

Background and summary of invention Recent years -have witnessed a phenomenal growth in the development and application of catalytic hydrocracking processes. By far the greatest part of these efforts have been directed toward methods for converting gas oils to products boiling in the gasoline range. The best catalysts developed to date for this purpose are those comprising a highly active cracking base, e.g. of the crystalline zeolite type, combined with a highly active hydrogenation component such as palladium or platinum. These catalysts are highly efficient fo-r converting middle distillate oils boiling in the 40G-750 F. range to gasoline. Due to the extensive use, and prospective use, of middle distillate stocks as feed to these gasoline-producing hydrocracking units, and to other economic, geographic and seasonal factors, a need is being felt in the industry to provide additional middle distillate stocks to meet the demand for other products such as turbine fuels and diesel fuels. An obviously desirable source of such additional middle distillate stocks comprises the heavy distillates boiling above about 700 F., which have heretofore been diverted largely to fuel oils because of the lack of an economica] method for converting them to lower boiling products.

In the initial investigation of hydrocracking techniques for converting 700 F.-{- hydrocarbon feeds to lower boiling materials, it became apparent that deep hydrocracking to produce gasoline in a single conversion step 'was impractical, firstly because inordinate amounts of butanes and dry gas were produced, and secondly because the gasoline product was always of extremely low octane quality. It became apparent therefore that for purposes of gasoline production, hydrocracking techniques were of primary value in connection 'with middle distillate feedstocks, and that the hydrocracking of higher boiling stocks would be feasible only if conversion to gasoline could be minimized and the production of middle distillates maximized. A primary objective in the hydrocracking of these heavy feeds thus *became to obtain maximum middle distillate/ gasoline ratios in the resulting product.

It was then found that the catalysts most useful for converting middle distillates to gasoline were least useful ICC for converting heavy feedstocks selectively to middle distillates, in that large amounts of dry gases, butanes and gasoline were produced. A great many conventional hydrocracking catalysts were tested in an attempt to find one which would convert such feedstocks more selectively to middle distillate products. In all cases it was found that the desired selectivity could be maintained only by operating at very low overall conversion rates, entailing prohibitively high recycle rates. But, on testing certain catalysts not conventionally regarded as hydrocracking catalysts, substantially more promising results were obtained. Specifically, it was found that by using a type of catalyst commonly employed for catalytic hydroning, composed of nickel and molybdenum oxides and/ or suldes supported on activated alumina, the selectivity of conversio-n to middle distillate products 'was excellent even at relatively high conversions of e.g. 40-60 volumepercent per pass. Moreover, for feedstocks containing organic nitrogen, it was found that these catalysts were not only more selective, but more active (on the basis of ternperature required for a given total conversion) than even the most active hydrocracking catalysts based on zeolite cracking bases.

In attempting to utilize these nickel-molybdenum-alumina catalysts for the manufacture of an acceptable diesel fuel product, an initial problem was encountered of maintaining stable prod-uct quality over the entire hydrocracking temperature range required in a run length of practical duration. With a fresh catalyst, and operating at conventional pressures in the mange of about 800 to 1500 p.s.i.g. and initial temperatures in the range of about 740-760D F., it was found that a diesel product of acceptable cetane index was obtained. However, as the run progressed, and temperatures were increased (to maintain conversion) to levels in the range of about 7 80-800 F., the cetane index of the product declined markedly. It was found however that this obstacle could be overcome without destroying the desired selectivity of conversion by operating at pressures above about 2000 p.s.i.g. In sharp distinction to the runs carried out at pressures of 1500 p.s.i.g., runs carried out at 2500 p.s.i.g. were found to give a diesel fuel product of relatively constant, high cetane index over the entire range of operating temperatures from about 750 to 825 F.

It was found moreover that these high pressures could be maintained over the entire run length without encountering excessive hydrogen consumption, a result which is believed to be attributable at least in part to the selective poisoning effect of the organic nitrogen content of the feed. It will be yunderstood that in the manufacture of diesel fuel by hydrogenation, an acceptable cetane index can be achieved far short of complete hydrogenation of the aromatic hydrocarbon content thereof. Accordingly, it is economically desirable to limit hydrogen consumption to the amount required to give an acceptable cetane index. It was found that this `can be achieved in the present process by maintaining throughout the conversion zone at least about 5 parts per million (based on feed) of organic nitrogen. Accordingly, as a process control feature, it is desirable to limit denitrogenation so that the liquid product always contains more than about 5 p.p.m. of organic nitrogen.

Brief description of drawing The attached drawing is a series of graphs depicting the principal experimental results of Examples VII, VIII and IX herein, illustrating principally that pressures above 2000 p.s.i.g. are required in order to obtain acceptable diesel fuel quality over a practical temperature range of about 740 to 825 F.

Description of feedstocks As will be apparent from the foregoing, the process of this invention is designed exclusively for the hydrocracking of mineral oil feedstocks containing a substantial proportion, preferably a Amajor proportion, of hydrocarbons having a true boiling point above about 700 F., and up to about 1200 F. Specifically preferred feedstocks are those containing less than about volumepercent of material boiling below 650 F., at least about 70 volume-percent of material boiling between 700 and 1000 F., and at least about 20 volume-percent of material boiling above 800 F. Feedstocks of this nature cannot be distilled at atmospheric pressure without substantial decomposition; they are normally derived from the vacuum distillation of crude oils, or by the deasphalting of residual oils. The heaviest fractions of catalytic cracking cycle oils, coker distillates and/or thermally cracked oils may also be utilized, either alone or in admixture with the preferred straight-run vacuum distillates or deasphalted residual oils. These feedstocks will normally contain at least about 10 weight-percent, and up to about 70 percent, of aromatic constituents, sulfur in amounts of about 0.01 to 3 percent by weight, and nitrogen in amounts of about 0.001 to 2 percent by weight. In the case of operations carried out at pressures above about 2000 p.s.i.g., it is specifically preferred to employ feeds containing at least about 100 p.p.m. of organic nitrogen in order to inhibit the complete hydrogenation of aromatic hydrocarbons.

The feedstocks and products described herein are characterized mainly on the basis of boiling range. Unless otherwise stated, when boiling ranges are given, atmospheric -boiling points are intended. Since the feedstocks cannot be distilled at atmospheric pressure, the atmospheric boiling ranges cited are calculated from standard ASTM D-1160 distillations carried out at 1 millimeter of mercury. The D-1160 distillation is operated essentially without reflux, and hence does not provide a sharp fractionation. For a more accurate determination of product yields and conversions, a true boiling point (TBP) distillation utilizing reflux is employed in the examples herein. The abbreviation TEBP as applied to the 700 F. end-point product refers to its true end boiling point.

Description of catalysts In broad aspect, operative catalysts for use herein may comprise any desired combination of nickel oxide and/ or sulfide plus an oxide and/or sulfide of molybdenum and/or tungsten, supported on a carrier composed essentially of activated alumina having a cracking activity index below about 25. Preferred catalysts comprise the sulfided forms of nickel-molybdenum-alumina containing about 1 5 weight-percent Ni and 4-25 percent Mo. Such catalysts are conventional in the art and hence need not be described in detail. They are normally prepared by impregnating tne alumina carrier with an aqueous solution or solutions of soluble salts of the respective metals, followed by draining, drying and calcining in air at temperatures up to about 800-1200" F. The calcined catalysts are preferably subjected to a presulding operation prior to contacting the feedstock, as by flowing a mixture of hydrogen and hydrogen sulfide through the catalyst bed at temperatures of e.g. 500 to 800 F.

The preferred carrier is activated alumina gel containing a minor proportion of coprecipitated silica gel. The silica content should not however exceed about 40 percent by weight; higher silica contents tend to increase the cracking activity to undesirably high levels. The preferred silica content is between about 3 percent and 25 percent by weight. Prior to impregnation, the carrier is preferably formed, as by extrusion or die-compression, into pellets of about 1/16JA-inch diameter. If desired however the catalyst may be employed in a powder form.

Process conditions OPERATING CONDITIONS Broad Preferred range range Pressure, p.s.i.g 500-5, 000 2, OOO-3, 500 Temperature, F.:

Start of run 650-800 725-780 End of run 750-850 G-840 LHSV, v./v o. 2-10 0. 5-2

Hz/Oil ratio, M s.c.f./b 2-20 4-10 The above conditions, primarily temperature, are suitably adjusted to maintain the desired degree of conversion per pass. Normally, conversions in the range of about 30-70 percent are desirable. As will be shown hereinafter, conversion levels above about 70 percent result in a marked increase in the ratio of gasoline, butane and dry gases produced, relative to the desired middle distillate product. A primary objective of the process is to maintain a volume ratio of 300-700 F. diesel fuel product to C5-300" F. gasoline of at least about 3/1. For this purpose, preferred conversion levels (based on true boiling points) normally lie in the range of about 35-65 percent to products boiling below the true 5 percent boiling point of the feed. Unconverted oil may be recycled to extinction if desired.

It is of primary economic concern to maintain a constant conversion to products of desired quality over an extended run length of at least about 30 days. To achieve this objective, the process is initiated at a relatively low temperature, and catalyst deactivation is compensated by periodically increasing the hydrocracking temperature. As will be shown hereinafter, where a constant high quality diesel fuel product is desired, this objective is difficult to achieve at pressures below about 2000 p.s.i.g. A specific objective of the process is hence to utilize pressures above about 2000 p.s.i.g., whereby a diesel fuel product of substantially constant cetane index between about 48 and 55 may be obtained over a run length of at least about 30 days, and encompassing a total temperature increase of at least 25 F. within the range of about 750-850 F. Further, it is desirable to achieve this objective without excessive hydrogen consumption.

It has been found that hydrogen consumption herein, resulting primarily from hydrogenation of aromatic hydrocarbons, is most readily controllable by two process variables: Hydrogen partial pressure, and the degree of denitrogenation achieved during hydrocracking. At pressures above about 2000 p.s.i.g., there is a tendency for extensive hydrogenation of aromatics to occur, a. tendency which can be overcome by maintaining at least about 5 p.p.m. of organic nitrogen (based on feed) throughout the contacting zone. For this purpose, it is preferred to employ feedstocks containing at least about p.p.m. of organic nitrogen, and to insure that at least about 5 p.p.m. of such nitrogen remains in the product efliuent. However, at pressures below about 2000 p.s.i.g., the catalysts of this invention do not appear to possess the required hydrogenation activity to effect excessive hydrogenation of aromatics, even in the absence of organic nitrogen. Hence, for operations carried out at below about 2000 p.s.i.g. feed nitrogen content is not so critical, though it may have a desirable effect in some cases.

The following examples are cited to illustrate the invention more specifically, but are not to be construed as limiting in scope:

Preface to examples In all the following examples, the same feedstock was employed, and the hydrocracking was carried out at a hydrogen/oil ratio of 7500 scf/barrel. The feedstock was a straight-run vacuum distillate analyzing as follows:

Nitrogen, wt. percent 0.387 Aromatics, wt. percent 35.2

Examples I through VI illustrate primarily the improved selectivity of conversion to middle distillate products obtained with the catalysts of this invention, as compared to more conventional hydrocracking catalysts. Examples VII through IX illustrate primarily the critical effect of pressure for maintaining a high quality diesel fuel product over a wide range of temperatures.

In all the examples, Conversion to 700 F. TEBP Products refers to actual feed disappearance, i.e., 100 minus the volume-percent of feed recovered as product having a true initial boiling point of 700 F. The Diesel/Gasoline Ratio refers to the volume ratio in the product of 30G-700 F. boiling range (TBP) diesel fuel to C-300" F. gasoline.

EXAMPLE I TABLE 1 Pressure, p.s.1.g

Conversion to 700 F. TEBP products, v 49. 6 56.8 Diesel/gasoline ratio in product, v 6. l 5.0 Hydrogen comsumption s .c.f.[b 1, 276 2K, 054 Cr-Ca gas make, s.c.f./b .1 4. 3 Butanes, vol. Iercant of f eed. 1. 4 1. 7 Diesel fuel pro uc 1 Yield, volV percent of feed 46. 6 52. 8

C etane index 48. 2 47. 2

Nitrogen, p.p.m 130 60 The foregoing illustrates a desirable selective conversion to diesel fuel, with a minimum production of lighter materials.

EXAMPLE II The operation described in Example I was 'continued at higher temperatures and pressures to obtaln an undesirably high overall conversion, with the followlng results:

TABLE 2 Run No I-C I-D Catalyst age, hrs 284308 364'376 LHSV,v./v.... 0.5 0.5 Temp., F 825 850 Pressure, p.s.i.g 2,500 2,500 Conversion to 700 F. TEBP products, vol. percent. 74. 1 88. 4 Diesel/gasoline ratio in product, v./v 3. 7 2. 1 C1-C3 gas make, s.c.f./b 137 232 Butanes, vol. percent of feed. 3. 3 5.1 Diesel fuel product:

Yield, vol. percent of feed. 64. 7 66. 9 Cetane index 50. 0 47.6 Nitrogen, p.p.m 10 10 The foregoing demonstrates that, even when using the preferred catalysts of this invention, the desired selective conversion to diesel fuel is not obtainable at overall conversion levels above about 70%. The production of dry gas, butanes and gasolines was much higher than in Example I.

EXAMPLE III The above feedstock was subjected to hydrocracking under several different run conditions using another catalyst of this invention comprising a presulded composite of 4.5 weight-percent Ni and 13 weight-percent M003 supported on an alumina-silica cogel base containing 14 weight-percent of silica, in the form of l/l-inch extruded pellets. The principal conditions and results were as follows:

TABLE 3 Run N o.

II-A II-B II-C II-D Catalyst age, hrs 42-66 90-114 330'351 10S-210 L v,y./v 1.0 1.0 1.0 1.0 Temp., F. 760 785 790 800 Pressure., p.s.i.g 1, 500 1, 500 1, 500 1,500 Converslon to 703 F. TEBP prod' ucts, vol. percent 33.0 45. 4 49. 0 56. 6 Dlesel/gasoline ratio in product, v./v 9. 1 6.0 5. 1 4. 7 Hydrogen consumption, s.c.I./b... 662 774 686 935 C1-C3 gas make, s.c.f./b 40. 1 73. 7 86. 2 98. 3 Butanes, vol. percent offeed 0.7 1. 3 1. 3 1. 5 Diesel Fuel Product:

Yield, vol. percent of feed 31. 7 42. 2 41. 0 50.0 Cetane index 47.0 45.0 46. 5 45. 0 Nitrogen, p.p.m 220 50 80 65 The above data again illustrates a desirable selective conversion to diesel fuel product with minimum conversion to gasoline and lighter materials. It will be noted however that at the 1500 p.s.i.g. pressure, the quality of the diesel fuel product was relatively low.

EXAMPLE IV Hydrocracking as described in Example III was continued at an elevated pressure of 2500 p.s.i.g., with the following results:

TABLE 4 Run No.

II-E II-F Catalyst age, hrs 471496 543-567 LHSV, v./v 0.5 0.5 Temp., F.. 790 825 Pressure, p.s. .g 2, 500 2, 500 Conversion to 700 F. TEBP product 58. 4 80. 9 Diesel/gasoline ratio in product, v./v 5.0 3. 1 CrCa gas make, s.c.f./b 70. 7 145.0 Butaues, vol. percent of feed 1.8 3.1 Diesel Fuel Product:

Yield, vol. percent of feed 54. 5 66. 7 Cetane index 51. 1 50.8 Nitrogen, p.p.m 10 10 The foregoing data shows that good diesel fuel quality can be maintained at temperatures up to 825 F. at a pressure of 2500 p.s.i.g. It is again noted however that the high conversion level of 80.9 percent results in decreased selectivity of conversion to middle distillate product.

EXAMPLE V The above feedstock was hydrocracked under several different run conditions utilizing a catalyst of known high hydrocracking activity consisting of 10 percent nickel and 0.47 weight-percent palladium supported on a cornposite of 20 weight-percent alumina and 80 weight-percent of mixed magnesium-hydrogen Y zeolite cracking base wherein about 50 percent of the ion exchange ca- Although the catalyst of this example was superior to that of Example V, it was still substantially inferior to the catalysts of this invention in that the selectivity of conversion to diesel fuel was relatively low, and the diesel pacity was satisfied by hydrogen ions and 40 percent by 5 fuel quality was low at all total conversion levels above magnesium ions. The principal conditions and results 26.6 percent were as follows:

TABLE Correlation of data from Examples I-VI Run N o.

HI B m C In order to obtain a more meaningful comparison between the catalysts utilized in Examples I to VI, the data 3' 2 -310 Catalystvge hrs O BO 298 1,0 from the 1500 p.s.i.g. runs was plotted in graph form so 0 fgfl'ep si'g uuul 1,500 LESS 1,233 15 that the results obtainable at a constant overall converonveision to 7 0 pro uc DWL/pere?, 7 ggg sion level of 50 percent could be picked off the resulting icsel gaso inc ratio in pro uct, v. v Hydrogen Consumption' s c'flbn 454 581 1,076 curves It will be understood that data 'relative-.nto product Ci-Cagas makeS-f-/b-un 233 54.5 4.4 qualityV and selectivity of conversion is meaningful only Butanes, vol. percent of feed 0.6 1. 4 5. 5 Diesel iuei product: when the comparisons are made at a constant overall Yield, vol. percent of feed 23.1 27. 1 35. 4 oetaneindex 6.3 44.3 42.2 conversion level. The results of this correlation were as 2 2 110 Nitrogen, p p m ,330 follows:

TABLE 7 (Ex VI) (Ex. I) (Ex. III) (Ex. V) Ni-Mo-i0 (Et-Y Ni-Mo-Al203 Ni-Mo-Al203 Ni-H-Y Zeo lite) 90 Catalyst 3.2% S104 14% S104 zeolite (eroi-A1203) Temp. required for conversion to 750 F. TEBP products, F 793 790 820 820 Diesel/gasoline ratio at 50% conversion, v./v 6. 4 6. 5 1. 8 4. 1 Ci-C; gas make, S.c../b 80 80 110 100 Butanes, vol. percent oi feed.... 1. 5 1. 4 4. 5 1. 7 Diesel fuel product:

Yield, vol. percent of feed..- 46. 4 46. 5 33. 0 41. 0 Ceran@ index 47.1 45. 9 42. 3 44. 3 Nitrogen, p.p.m 120 110 100 740 The above data shows that zeolite catalyst gave poor selectivity of conversion to diesel fuel at all conversion levels above about 30 percent. At 57.6 percent conversion, large amounts of gasoline and lighter products were produced. The quality of the diesel fuel product was relatively low at all conversion levels.

EXAMPLE VI The above feedstock was hydrocracked under several different run conditions utilizing another known hydrocracking catalyst of high activity, composed of 4 weightpercent NiO and 15 weight-percent M003 supported on a steamed composite of (A) about 90 Weight-percent amorphous silica-alumina cogel (90% SiO2-l0% A1203), and (B) about 10 weight-percent of hydrogen Y zeolite. The principal conditions and results of the runs were as follows:

TABLE 6 Run No.

IV-A IV-B IV-C IV-D Catalyst age, hrs 46-70 118-142 190-21 238-262 LHSV, v./v` 1.0 1.0 1.0 1.0 Temp., 760 790 825 850 Pressure, p.s.i-g 1, 500 1, 500 1, 500 1, 500 Conversion to 700 F.TEPB products, vol. percent 26. 6 35.1 54. 7 59. 9 Diesel/gasoline ratio in product,

v. 13. 4 5. 7 4. 4 3.3 Hydrogen consumption, s.c.i./b 978 1, 185 1, 155 1, 050 C1-C3 gas make S.e.f./b 27. 3 56.4 1,144 162, 5 butanes, vol. percent of leed 0. 5 1 3 1. J 2.8 Diesel fuel product:

Yield, vol. percent oi feed 26.7 31.8 47. 7 48. 6 Cetane index 48.3 45. 5 44. 0 42. 9 Nitrogen, p.p.m 1,070 550 730 770 From the foregoing data, the following points are evident: (1) the catalysts of Examples I and III gave the same overall conversion at much lower temperatures than did the presumably more active catalysts of Example V and VI; (2) the diesel/gasoline ratios obtainable with the present catalysts were considerably higher than the ratios obtained with the zeolite catalysts, and moreover the production of light gases and butanes was lower; (3) higher quality diesel fuel is obtainable with the present catalysts than can be obtained with the zeolite catalysts.

EXAMPLE VII To evaluate the eifect of a low-pressure operation, the above feedstock was subjected to hydrocracking at 600 p.s.i.g. and various temperatures, using as the catalysts a presulded composite of 3.3 weight-percent NiO, 0.225 weight-percent CoO and 15.3 percent M003, supported on an alumina-silica cogel containing 4.4 Weight-percent SiOz. The results of these runs were as follows:

TABLE 8 Run N o.

V-A V-B V-C Median catalyst age, hrs 646 478 550 Pressures p.s .i.g 600 600 600 Tem 725 760 800 LHS 1.0 1.0 1.0 Conversion to 700 F. TEBP products, vol. perce t 20. 5 33. 4 51. 3 Diesel/gasoline ratio in product, v./v 17. 0 8. 4 5. 6 Hydrogen consumption, s.c.f./b 522 413 552 Ci-C3 gas make, s.c.f./b 24. 4 60. 7 128. 0 Butanes, vol. percent of feed 0. 5 0. 9 1. 8 Diesel uel product:

Yield, vol. percent oi Iced 21. 1 30. 3 43. 6 Cetane index 48. 1 46.0 43. 8 Nitrogen, p.p.m 2, 320 1, 880 1, 540

It is apparent from the foregoing that at low pressures, adequate diesel fuel quality is obtainable only at very low conversion levels and temperatures. Moreover, denitrogenation was inadequate (it is normally desirable to achieve at least about 80-90% denitrogenation), and the dry gas make was relatively high.

-EXAMPLE VIII Hydrocracking as described in Example VII was continued at an increased pressure of 1500 p.s.i.g. and at varying temperatures, with the following results:

TABLE 9 Run No.

V-D V-E V-F V-G V-H Median catalyst, age hrs 332 289 169 337 244 Pressure, p.s.i.g 1, 500 l, 500 1,500 1,500 1,500 emp., 650 700 725 760 800 LHSV, V /V... 1.0 1.0 1.0 1.` 1.0 Conversion to 700 F EBP pro ucts, vol. percent 19.0 21. 2 25. 3 38.0 59.0 Diesel/gasoline ratio in product, n

v. v 8.1 17.5 12.8 8.5 4.8 Hydrogen consumption, s.c.f./b 256 571 847 915 1,131 Ct-Cr gas make, s.c.f/.b 14. 3 14. 9 21.1 47 109 Butanes, vol. percent of feed 0.5 0.3 0.4 1.9 1.5 Diesel fuel product:

Yield, vol. percent of feed. 17. 1 21.1 25. 6 36. 6 52. 9 C etane index 47. 0 49.0 48. 9 48. 6 44. 8 Aromatics, wt. percent. 42.0 40. 4 38. 3 39. 6 40. 5 Nitrogen, p.p.m 1,460 469 214 63 The more significant data reported above is depicted in graph form in the attached drawing. It will be noted that acceptable cetane indexes above 48 were obtainable at 1500 p.s.i.g. over a fairly broad temperature range of about 680-770 F. However, within this temperature range, minimally adequate conversion levels of about 30- 42 volume-percent were obtainable only over the narrow temperature range of about 750-770 F. At more desirable conversion levels above 42 percent, the cetane index dropped off very rapidly. It is evident therefore that at 1500 p.s.i.g. it would not be practical to maintain acceptable diesel fuel quality, even at minimally acceptable conversion levels, except over very short run lengths.

EXAMPLE IX The hydrocracking operation described in Example VIII was continued at an elevated pressure of '2500 p.s.i.g. and at various temperatures, with the following results:

TABLE Run No,

V-K V-L V-M Median catalyst age, hrs 164 224 296 Pressure, p.s.i.g. 2,500 2,500 2,500 em F 725 760 800 LHS 1. 0 1. o 1. c Conver vol. percent 23.2 24.5 35. 2 62.0 Diesel/gasoline ratio in product, v./v 20. 3 13. 7 7. 7 4. 6 Hydrogen consumption, s.c.f./b 777 1,066 1,192 1,446 Cr-Cs gas make, s.c.f./b 15. 9 23. 2 41.0 7.0 Butanes, vol. percent of feed 0.6 0. 6 0.7 3. 0 Diesel fuel product:

Yield, vol. percent of feed 22. 3 24. 7 35. 4 55. 6 Cetane index 49. 7 50. 3 50. 3 50. 9 Aromatics, wt. percent.. 36. 3 31. 5 22.7 19. 3 Nitrogen, p.p.m 293 89 30 23 The foregoing data is likewise plotted in the drawing, and it will be seen that only in this case was it possible to achieve high diesel fuel quality at high conversion levels, and over a substantial temperature range. Moreover, it will be noted that these results were obtained with no significant change in selectivity of conversion, and with -a reduced dry gas make. The increased pressure employed in this example did effect some increase in aromatics hydrogenation, but if the conditions had been altered so as to reduce the nitrogen content to below about 5 parts per million, aromatics hydrogenation would have been substantially complete, with resultant increased hydrogen consumption.

The foregoing details as to catalysts and process conditions are not intended to be limiting in effect. The following claims and their reasonable equivalents are intended to define the true scope of the invention:

I claim:

1. A method for the catalytic hydrocracking of a heavy mineral oil feedstock boiling predominantly above 700 F. over an extended run length of at least about 30 days and at hydrocracking temperatures progressively increasing a total of at least about 25 F within the temperature range of 750-850 F., while recovering as the major product from said hydrocracking a diesel fuel fraction boiling mainly between about 300 and 700 F. having a relatively constant cetane index above about 48, which comprises contacting said feedstock plus added hydrogen and at a pressure between about 2000 and 3500 p.s.i.g., with a catalyst consisting essentially of a minor proportion of nickel oxide and/or sulfide, a minor proportion of an oxide and/or sulfide of molybdenum and/or tungsten, and a major proportion of a carrier comprising essentially activated alumina having a cracking Activity Index below about 25.

2. A method as defined in claim 1 wherein said hydrocracking temperature is adjusted and correlated with space velocity to maintain a relatively constant total conversion of about 30-70 volume-percent of feed material boiling above 700 F. to products boiling below 700 F., said liquid products boiling below 700 F. comprising at least about 3 volumes of diesel fuel boiling in the 300- 700 F. range for each volume of C5-300" F. boiling range material.

3. A method as defined in claim 1 wherein said catalyst comprises essentially a minor proportion of nickel sulfide and a minor proportion of molybdenum sulfide supported upon an activated alumina carrier containing about 3-40 percent by weight of coprecipitated silica gel.

4. A method as defined in claim 1 wherein the feedstock contains at least about p.p.m. of organic nitrogen, and wherein the conditions of hydrocracking are adjusted to give a product still containing at least about 5 p.p.m. of organic nitrogen, whereby hydrogenation of aromatics is minimized.

5. A method as defined in claim 1 wherein said feedstock is essentially a straight run vacuum distillate containing less than about l0 volume-percent of material boiling below 650 F., at least about 70 volume-percent of material boiling between 700 and 1000 F., and at least about 20 volume-percent of material boiling above 800 F.

6. A method as defined in claim 1 wherein unconverted oil from said hydrocracking boiling above 700 F. is continuously recycled thereto.

7. The method of hydrocracking relatively heavy hydrocarbons boiling predominately above about 700 F. and containing at least about 100 p.p.m. organically bound nitrogen to middle oil fuels of relatively consistent quality at a relatively constant conversion rate to said middle oil fuels which comprises contacting said hydrocarbons with a catalyst consisting essentially of about l to about 5 weight percent nickel oxide and/or sulfide and about 4 to about 25 weight percent of at least one of the oxides and sulfides of molybdenum and tungsten combined with an activated alumina carrier having a cracking activity index below about 25 at a ternperature within the range of about 650 to about 850 F., a pressure of at least about 2000 p.s.i.g. and a liquid hourly space velocity within the range of about 0.2 to about 10 in the presence of about 2000 to about 20,000 s.c.f. of hydrogen per barrel of said hydrocarbon over an extended period of at least about 30 days, said temperature, pressure, space velocity and hydrogen content being correlated to produce a product of relatively constant cetane index containing at least about 5 p.p.m. organic nitrogen, and gradually increasing said temperature at which said hydrocarbons are contacted with said 1 1 catalyst during said run length by at least about 25 F. to maintain said relatively constant conversion to said middle oil fuels.

8. The method of claim 7 wherein less than about 10 percent of said hydrocarbon feed boils below about 650 F., at least about 70 percent of said hydrocarbon feed boils within the range of about 700 to about 1000 F. and at least about 20 percent of said feed boils at a temperature above about 800 F., and said hydrocarbon feed contains at least about 10 weight percent aromatic hydrocarbons and about 0.001 to about 2 weight percent or ganically bound nitrogen.

9. The method of claim 7 wherein less than about 10 percent of said hydrocarbon feed boils -below about 650 F., at least about 70 percent of said hydrocarbon feed -boils within the range of about 700 to about 1000 F. and at least about 20 percent of said hydrocarbon feed boils at a temperature above about 800 F., said alumina carrier contains about 3 to about 25 weight percent silica, and said hydrocarbon is contacted with said catalyst at a pressure within the range of about 2000 to about 3500 p.s.i.g., a liquid hourly space velocity within the range of 0.5 to about 2 in the presence of about 4000 to about 10,000 standard cubic feet of hydrogen per barrel of said hydrocarbon.

10. The method of claim 7 wherein at least about 70 percent of said hydrocarbon Iboils within the range of about 700 to about 1000 F., said hydrocarbon is contacted with said catalyst at a pressure within the range of about 2000 to about 3500 p.s.i.g., a liquid hourly space velocity within the range of about 0.5 to about 2 in the presence of about 4000 to about 10,000 feet of hydrogen per barrel of said hydrocarbon at a reaction temperature within the range of about 725 to about 840 F. to produce a mid barrel fuels product at a relatively constant conversion level having a cetane index of at least about 48 and a total hydrocarbon product containing at least about 5 p.p.m. organically bound nitrogen.

References Cited UNITED STATES PATENTS 2,848,376 8/ 1958 Oettinger et al. 208-57 3,340,180 9/1967 Beuther et al. 208-112 3,369,995 2/1968 Tupman et al. 208-112 DELBERT E. GANTZ, Primary Examiner ABRAHAM RIMENS, Assistant Examiner U.S. Cl. X.R. 208-59 

